An actuator using a piezoelectric ceramic uses such a piezoelectric effect that when an electric field is applied, mechanical strain and stress will be generated. The actuator has such characteristics that a very small displacement can be obtained with high accuracy, and generated strain is large, and, for example, the actuator is used to position a precision tool or an optical device. As a conventional piezoelectric ceramic used for the actuator, lead zirconate titanate (PZT) having excellent piezoelectric properties is used most often. However, lead zirconate titanate contains a large amount of lead, so adverse effects on global environment such as lead leaching due to acid rain have become controversial. Therefore, the development of piezoelectric ceramics not including lead instead of lead zirconate titanate is desired.
As the piezoelectric ceramic not including lead, for example, a piezoelectric ceramic including barium titanate (BaTiO3) as a main component is known (refer to Japanese Unexamined Patent Application Publication No. Hei 2-159079). The piezoelectric ceramic is superior in a high relative dielectric constant ∈r and a high electromechanical coupling factor kr, so the piezoelectric ceramic holds promise as a piezoelectric material for the actuator. Moreover, as another piezoelectric ceramic not including lead, for example, a piezoelectric ceramic including potassium sodium lithium niobate as a main component is known (refer to Japanese Unexamined Patent Application Publication No. Sho 49-125900 or Japanese Examined Patent Application Publication No. Sho 57-6713). The piezoelectric ceramic has a high Curie temperature of 350° C. or over, and an excellent electromechanical coupling factor kr, so the piezoelectric ceramic holds promise as a piezoelectric material. Further, a compound including potassium sodium niobate and a tungsten bronze-type oxide has been recently reported (Japanese Unexamined Patent Application Publication No. Hei 9-165262).
However, the piezoelectric ceramics not including lead have such a problem that they have lower piezoelectric properties, compared to lead-based piezoelectric ceramics, so a sufficiently large amount of generated displacement cannot be obtained. Moreover, in the piezoelectric ceramic including barium titanate as a main component, barium titanate has a low Curie temperature of approximately 120° C., so there is such a problem that an operating temperature range is limited to 100° C. or less. Further, in the piezoelectric ceramic including sodium lithium potassium niobate as a main component, sodium, potassium and lithium are easily volatilized during sintering, so there is such a problem that it is difficult to sinter the piezoelectric ceramic.
In view of the foregoing, it is an object of the invention to provide a piezoelectric ceramic with a wider operating temperature range capable of obtaining a large amount of generated displacement, and capable of being easily sintered, and being superior in the point of ultra-low emission, environmental friendliness and ecology.